1. Field of the Invention
The present invention relates a thin film magnetoresistive (MR) read transducer and, more particularly, to an arrangement of leads for an MR read transducer which enables cancellation of thermal asperity noise upon contact of the transducer with moving magnetic media.
2. Description of the Related Art
An MR read transducer employs an MR stripe or layer which changes resistance in response to magnetic flux incursions from a moving magnetic medium, such as a rotating magnetic disk. A sense current, which is passed through the MR stripe, varies proportionately with changes in resistance of the MR stripe. The response of the MR stripe is based on how well the resistance change follows the change in flux density sensed from the magnetic medium.
In a conventional read head configuration, the MR stripe is a thin film layer which is sandwiched between bottom and top insulation layers G1 and G2 which, in turn, are sandwiched between bottom and top shield layers S1 and S2. The distance between the shield layers is called the "read gap". The smaller the read gap, the greater the resolution of the MR read transducer. The MR read transducer has considerable promise for handling the high data rates being developed by present technology.
One of the problems encountered with MR read transducers is that large signal transients are generated in an MR stripe by contact of the transducer with asperities on the magnetic medium. This is referred to as "thermal asperity noise". When the transducer contacts asperities on a rotating disk, for example, heat is generated within the MR stripe, which changes its resistance to produce a large signal transient. In a disk drive, such signal transients are reflected as noise when the readback signal generated by the transducer is amplified.
Another problem with MR read transducers is that electrical shorting can occur between an air bearing surface (ABS) of the transducer and the magnetic storage medium. If the ABS of the transducer is not at the same potential as the medium, then on contact between the two a current flows between the sensor and medium. The likelihood of a short is increased by contact or near-contact with the storage medium. In the event of a single short, the MR read transducer can be severely damaged, rendering it inoperable. The higher the potential difference between the MR read transducer and the medium, the greater the risk of damage to the transducer.
Still another problem of an MR read transducer is that shorting may occur between the shields S1 and S2 and the MR stripe when the shields are constructed of NiFe. The shorting occurs during head-disk contact during operation when the NiFe from the shields, which is conductive, is smeared across the ABS. This renders the head inoperable unless the portion of the MR stripe exposed at the ABS is at or nearly at an equipotential. The prior art overcomes this problem by constructing the shields of Sendust, which is resistant to smearing. Sendust requires high temperature processing, which has been shown to greatly increase stress in the substrate, thereby requiring much tighter control of the MR stripe magnetostriction. Sendust also introduces noise during quasistatic testing of the MR read transducer. On the other hand, NiFe requires relatively simple processing steps, is easy to incorporate into a head manufacturing process, and would be preferable to Sendust, with a solution to the shorting problem.